Increasing world energy demand is creating unprecedented challenges for recovering energy resources, and mitigating the environmental impact of using those resources. Some have argued that the worldwide production rates for oil and domestic natural gas will peak within a decade or less. Once this peak is reached, primary recovery of oil and domestic natural gas will start to decline, as the most easily recoverable energy stocks start to dry up. Historically, old oil fields and coal mines are abandoned once the easily recoverable materials are extracted. These abandoned reservoirs, however, still contain significant amounts of carbonaceous material. The Powder River Basin in northeastern Wyoming, for example, is still estimated to contain approximately 1,300 billion short tons of coal. Just 1% of the Basin's remaining coal converted to natural gas could supply the current annual natural gas needs of the United States (i.e., about 23 trillion cubic feet) for the next four years. Several more abandoned coal and oil reservoirs of this magnitude are present in the United States.
As worldwide energy prices continue to rise, it may become economically viable to extract additional oil and coal from these formations with conventional drilling and mining techniques. However, a point will be reached where more energy has to be used to recover the resources than can be gained by the recovery. At that point, traditional recovery mechanisms will become uneconomical, regardless of the price of energy. Thus, new recovery techniques are needed that can extract resources from these formations with significantly lower expenditures of energy and costs.
One route for light hydrocarbon recovery that has received little commercial attention is biogenic conversion of carbonaceous materials in geologic formations into methane. As noted above, large potential sources of methane and other hydrocarbons with enhanced hydrogen content are locked up in the carbonaceous materials in coal, residual oil, etc. In biogenic conversion, microorganisms in the formation treat these carbonaceous materials as a food source and metabolize them into metabolic intermediates and products, such as alcohols, organic acids, aromatic compounds, hydrogen and methane, among others.
In many formations, however, the environmental chemistry does not favor the biogenic production of metabolic products like hydrogen and methane. In some of these formations, the presence of an inhibitor (e.g., saline) can prevent the microorganisms from metabolizing the carbonaceous substrate into the products. In other formations, the low concentration of one or more compounds (e.g., nutrient compounds) in the formation environment can slow or stop biogenic production of the products. In still other formations, a rise in concentration of a metabolic intermediate or product generated by an active consortium of microorganisms can slow additional metabolic activity.
Thus, there remains a need to identify chemical compounds that effect the rate of biogenic production of metabolic products by microorganisms in a formation environment. There also remains a need for methods of introducing chemical amendments to a geologic formation that will stimulate the biogenic production of the metabolic products. These and other needs are addressed by the present invention.